deprecated boost::unordered::hash_is_avalanching in favor of boost::hash_is_avalanching (#313)

* deprecated boost::unordered::hash_is_avalanching in favor of boost::hash_is_avalanching

* replaced deprecation message with simpler BOOST_HEADER_DEPRECATED

doc/modules/ROOT/pages/changes.adoc

@@ -8,6 +8,10 @@
 
 == Release 1.89.0
 
+* Deprecated `boost::unordered::hash_is_avalanching` is now a using-declaration of
+`boost::hash_is_avalanching` in `<boost/container_hash/hash_is_avalanching.hpp>`.
+Use that header directly instead. `<boost/unordered/hash_traits.hpp>` will be
+removed in the future.
 * Added `pull(const_iterator)` to open-addressing containers. This operation
 allows for efficient removal and retrieval of an element via move construction.
 

doc/modules/ROOT/pages/hash_quality.adoc

@@ -43,7 +43,8 @@ struct my_string_hash_function
 ----
 
 By setting the
-`xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]` trait, we inform Boost.Unordered
+`link:../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]`
+trait, we inform Boost.Unordered
 that `my_string_hash_function` is of sufficient quality to be used directly without
 any post-mixing safety net. This comes at the risk of degraded performance in the
 cases where the hash function is not as well-behaved as we've declared.

doc/modules/ROOT/pages/rationale.adoc

@@ -102,7 +102,8 @@ and *high* and *low* are the upper and lower halves of an extended word, respect
 In 64-bit architectures, _C_ is the integer part of 2^64^∕https://en.wikipedia.org/wiki/Golden_ratio[_φ_],
 whereas in 32 bits _C_ = 0xE817FB2Du has been obtained from https://arxiv.org/abs/2001.05304[Steele and Vigna (2021)^].
 
-When using a hash function directly suitable for open addressing, post-mixing can be opted out of via a dedicated `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]` trait.
+When using a hash function directly suitable for open addressing, post-mixing can be opted out of via a dedicated 
+`link:../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]` trait.
 `boost::hash` specializations for string types are marked as avalanching.
 
 === Platform Interoperability

doc/modules/ROOT/pages/reference/concurrent_flat_map.adoc

@@ -364,7 +364,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/concurrent_flat_set.adoc

@@ -311,7 +311,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/concurrent_node_map.adoc

@@ -381,7 +381,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/concurrent_node_set.adoc

@@ -328,7 +328,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/hash_traits.adoc

@@ -7,39 +7,22 @@
 
 [listing,subs="+macros,+quotes"]
 -----
+#include <boost/container_hash/hash_is_avalanching.hpp>
+
 namespace boost {
 namespace unordered {
 
-template<typename Hash>
-struct xref:#hash_traits_hash_is_avalanching[hash_is_avalanching];
+using boost::hash_is_avalanching;
 
 } // namespace unordered
 } // namespace boost
 -----
 
----
-
-=== hash_is_avalanching
-```c++
-template<typename Hash>
-struct hash_is_avalanching;
-```
-
-A hash function is said to have the _avalanching property_ if small changes in the input translate to
-large changes in the returned hash code &#8212;ideally, flipping one bit in the representation of
-the input value results in each bit of the hash code flipping with probability 50%. Approaching
-this property is critical for the proper behavior of open-addressing hash containers.
-
-`hash_is_avalanching<Hash>::value` is:
-
- * `false` if `Hash::is_avalanching` is not present,
- * `Hash::is_avalanching::value` if this is present and convertible at compile time to a `bool`,
- * `true` if `Hash::is_avalanching` is `void` (this usage is deprecated),
- * ill-formed otherwise.
- 
-Users can then declare a hash function `Hash` as avalanching either by embedding an appropriate `is_avalanching` typedef
-into the definition of `Hash`, or directly by specializing `hash_is_avalanching<Hash>` to a class with
-an embedded compile-time constant `value` set to `true`.
+[horizontal]
+Note:;; This header is deprecated. Use instead
+`link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[boost::hash_is_avalanching]`
+defined in
+`link:../../../../../container_hash/doc/html/hash.html#ref_boostcontainer_hashhash_is_avalanching_hpp[<boost/container_hash/hash_is_avalanching.hpp>]`.
 
 Open-addressing and concurrent containers
 use the provided hash function `Hash` as-is if `hash_is_avalanching<Hash>::value` is `true`; otherwise, they

doc/modules/ROOT/pages/reference/stats.adoc

@@ -66,6 +66,7 @@ If the supplied hash function has good quality, then:
 * For unsuccessful lookups, the average number of element comparisons should be close to 0.0.
 
 These statistics can be used to determine if a given hash function
-can be marked as xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[__avalanching__].
+can be marked as 
+link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[__avalanching__].
 
 ---

doc/modules/ROOT/pages/reference/unordered_flat_map.adoc

@@ -317,7 +317,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/unordered_flat_set.adoc

@@ -266,7 +266,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/unordered_node_map.adoc

@@ -320,7 +320,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

doc/modules/ROOT/pages/reference/unordered_node_set.adoc

@@ -270,7 +270,7 @@ The size of the bucket array can be automatically increased by a call to `insert
 greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to
 allow for higher loads.
 
-If `xref:reference/hash_traits.adoc#hash_traits_hash_is_avalanching[hash_is_avalanching]<Hash>::value` is `true`, the hash function
+If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function
 is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing
 at the expense of extra computational cost.
 

include/boost/unordered/detail/foa/core.hpp

@@ -1,6 +1,6 @@
 /* Common base for Boost.Unordered open-addressing tables.
  *
- * Copyright 2022-2024 Joaquin M Lopez Munoz.
+ * Copyright 2022-2025 Joaquin M Lopez Munoz.
  * Copyright 2023 Christian Mazakas.
  * Copyright 2024 Braden Ganetsky.
  * Distributed under the Boost Software License, Version 1.0.
@@ -16,6 +16,7 @@
 #include <boost/assert.hpp>
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
+#include <boost/container_hash/hash_is_avalanching.hpp>
 #include <boost/core/allocator_traits.hpp>
 #include <boost/core/bit.hpp>
 #include <boost/core/empty_value.hpp>
@@ -28,7 +29,6 @@
 #include <boost/unordered/detail/mulx.hpp>
 #include <boost/unordered/detail/static_assert.hpp>
 #include <boost/unordered/detail/type_traits.hpp>
-#include <boost/unordered/hash_traits.hpp>
 #include <boost/unordered/unordered_printers.hpp>
 #include <climits>
 #include <cmath>
@@ -1426,7 +1426,7 @@ public:
   using size_policy=pow2_size_policy;
   using prober=pow2_quadratic_prober;
   using mix_policy=typename std::conditional<
-    hash_is_avalanching<Hash>::value,
+    boost::hash_is_avalanching<Hash>::value,
     no_mix,
     mulx_mix
   >::type;

include/boost/unordered/hash_traits.hpp

@@ -1,6 +1,6 @@
 /* Hash function characterization.
  *
- * Copyright 2022-2024 Joaquin M Lopez Munoz.
+ * Copyright 2022-2025 Joaquin M Lopez Munoz.
  * Distributed under the Boost Software License, Version 1.0.
  * (See accompanying file LICENSE_1_0.txt or copy at
  * http://www.boost.org/LICENSE_1_0.txt)
@@ -11,58 +11,15 @@
 #ifndef BOOST_UNORDERED_HASH_TRAITS_HPP
 #define BOOST_UNORDERED_HASH_TRAITS_HPP
 
-#include <boost/unordered/detail/type_traits.hpp>
+#include <boost/config/header_deprecated.hpp>
+#include <boost/container_hash/hash_is_avalanching.hpp>
+
+BOOST_HEADER_DEPRECATED("<boost/container_hash/hash_is_avalanching.hpp>")
 
 namespace boost{
 namespace unordered{
 
-namespace detail{
-
-template<typename Hash,typename=void>
-struct hash_is_avalanching_impl:std::false_type{};
-
-template<typename IsAvalanching>
-struct avalanching_value
-{
-  static constexpr bool value=IsAvalanching::value;
-};
-
-/* may be explicitly marked as BOOST_DEPRECATED in the future */
-template<> struct avalanching_value<void>
-{
-  static constexpr bool value=true;
-};
-
-template<typename Hash>
-struct hash_is_avalanching_impl<
-  Hash,
-  boost::unordered::detail::void_t<typename Hash::is_avalanching>
->:std::integral_constant<
-  bool,
-  avalanching_value<typename Hash::is_avalanching>::value
->{};
-
-template<typename Hash>
-struct hash_is_avalanching_impl<
-  Hash,
-  typename std::enable_if<((void)Hash::is_avalanching,true)>::type
->{}; /* Hash::is_avalanching is not a type: compile error downstream */
-
-} /* namespace detail */
-
-/* Each trait can be partially specialized by users for concrete hash functions
- * when actual characterization differs from default.
- */
-
-/* hash_is_avalanching<Hash>::value is:
- *   - false if Hash::is_avalanching is not present.
- *   - Hash::is_avalanching::value if this is present and constexpr-convertible
- *     to a bool.
- *   - true if Hash::is_avalanching is void (deprecated).
- *   - ill-formed otherwise.
- */
-template<typename Hash>
-struct hash_is_avalanching: detail::hash_is_avalanching_impl<Hash>::type{};
+using boost::hash_is_avalanching;
 
 } /* namespace unordered */
 } /* namespace boost */

test/unordered/hash_is_avalanching_test.cpp

@@ -1,10 +1,9 @@
 // Copyright 2022 Peter Dimov
-// Copyright 2024 Joaquin M Lopez Munoz
+// Copyright 2024-2025 Joaquin M Lopez Munoz
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
 // an imitation of a third-party header specializing hash_is_avalanching
-// (boost/container_hash/hash.hpp is an example doing that)
 
 #include <boost/type_traits/integral_constant.hpp>
 
@@ -13,14 +12,11 @@ struct X3
 };
 
 namespace boost
-{
-namespace unordered
 {
 
     template<class T> struct hash_is_avalanching;
     template<> struct hash_is_avalanching< ::X3 >: boost::true_type {};
 
-} // namespace unordered
 } // namespace boost
 
 //